The arrest of Damian Green, the shadow home office minister, is more than just worrying. It seems the police, operating on their own initiative, decided that the Tory frontbencher had allegedly broken the law for "aiding, abetting, counselling or procuring misconduct in public office".

What he was actually doing, as any good investigative journalist would know, is obtaining information that the government had suppressed of an extremely embarrassing nature that ministers would rather not see published.

To do this, it sounds like he had good Whitehall source, who was able to provide him with true information about the employment of thousands of illegal immigrants in Whitehall and one in parliament, an internal ministerial letter about the dangers of rising crime caused by the recession and a list of potential Labour rebel MPs over the anti terror laws.

None of these things would compromise national security – all of them, if aired in public, would probably contribute to action to get something done.

The police action does compromise the action of whistleblowers – a right that is enshrined in law by the Public Interest Disclosure Act, a private members act initiated by Tory MP, Richard Shepherd, one of the greatest friends of freedom of information . It was passed by the present Labour government in 1998. This gives immunity from prosecution for people who disclose information such as dangers to health and safety, breaches of the law, and miscarriages of justice.

While it may not cover this incident (leaking to an opposition spokesman does not qualify for immunity, though employing illegal immigrants is a breach of the law) – it reflects an honourable tradition of making public embarrassing information that has been covered up.

This makes the police action – as far as we know – sound very heavy. But the action is also very chilling to the normal terms of trade.

The fact is that whistleblowing happens every week and any government that thinks it can stop it is daft and stupid. If people behave hypocritically, if authorities turn blind eyes to dodgy and questionable behaviour, the only place where people can get an independent hearing is often the media.

Looking at Damian Green's "crime list" I can easily replicate it myself. I seem to remember getting sight of a list of Labour MPs who were going to vote for and against Gordon Brown for the leadership. I shouldn't have seen it, but I did. Should I, and the leaker, be prosecuted? I also got sight of a memo from Defra's permanent secretary, Dame Helen Ghosh, announcing serious cuts in the ministry's budget – at a time when Hilary Benn, the secretary of state, was making out they weren't any. Embarrassing but true, the leak forced Dame Helen to defend it publicly in front of the Commons select committee for her department. It was made public by people – yes, there was more than one – who felt the ministry was being dishonest and hypocritical over its planned spending over green issues.

Internal letters between ministers also do get leaked – particularly if ministers are not disclosing the full facts to the public. Civil servants, trade unions and MPs get information they should not have every week.

Perhaps this is why Damian Green is getting such a rough ride. The Establishment – and that includes Phil Woolas, who raised the absurd spectre of conspiracy on the Today programme – have a lot to be worried about and this action might suit their purposes to frighten people. But show trials over leakers are not part of British democracy, nor should they ever be.